Define new audio attribute flag: beacon

Flag AUDIO_FLAG_BEACON characterizes streams where the system
  ensures that the playback of the sound will be compatible
  with its use as a broadcast for surrounding people
  and/or devices. Ensures audibility with no or minimal
  post-processing applied.

Bug 15415971

Change-Id: I1df9dc50e3fcc973a0709a55df5b3bd95f81eb58
diff --git a/include/system/audio.h b/include/system/audio.h
index bf3dee7..5db2127 100644
--- a/include/system/audio.h
+++ b/include/system/audio.h
@@ -109,6 +109,7 @@
     AUDIO_FLAG_AUDIBILITY_ENFORCED = 0x1,
     AUDIO_FLAG_SECURE              = 0x2,
     AUDIO_FLAG_SCO                 = 0x4,
+    AUDIO_FLAG_BEACON              = 0x8
 };
 
 /* Do not change these values without updating their counterparts